Heat sealable film with linear tear properties

ABSTRACT

A monoaxially oriented film including a propylene-based random copolymer and at least about 3 wt % of a low density polyethylene which is oriented at least about 2.5 times in one direction and exhibits excellent linear directional tear properties parallel to the orientation direction and excellent heat seal performance in terms of high heat seal strengths and low seal initiation temperature. This film formulation and orientation is suitable for pouch applications requiring an “easy-tear” linear tear feature and excellent hermetic seal properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/368,796, filed Jul. 29, 2010, the contents of which isincorporated herein by reference.

FIELD OF INVENTION

This invention relates to a mono-oriented film that possesses lineartear properties. The films include a blend of an incompatible polymersuch as low density polyethylene (LDPE) with propylene-based randomcopolymers and/or terpolymers. The films, when mono-oriented, displaythe tendency to fibrillate.

BACKGROUND OF INVENTION

Polymer films are commonly utilized to produce containers, such aspouches, that are used to contain, transport, and preserve a variety ofsubstances, including but not limited to, foods. These containers arecommonly created using a heat sealing process, in which high pressureand temperature is applied to opposing polymer films or laminates tojoin them together. Through this sealing process, the shelf life of thepackaged material is extended through the prevention of contamination ofthe substance from such processes as microbial contamination or aninflux of gases such as oxygen (which can cause rancidity of somepackaged food products via oxidation of fats and oils) or water vapor(which can cause staleness of some packaged food products via moistureretention or loss). The temperature at which this seal is created can berelatively high depending on the melting or softening point of thepolymer material used as a sealant. The seal initiation temperature(SIT) of the sealant material can be important to commercial packagerssince it will influence the operating conditions (e.g. temperature setpoints) of the packaging machine as well as packaging speeds due tothermal transfer/residence time for the heat from the sealer jaws tosoften and fuse the package's sealant material. In general, a lower SITis desirable as it can allow lower temperature settings for the heatedjaw sealers of the packaging machine. By reducing this seal initiationtemperature, the process can be made to be faster, more economical, useless electricity, and be more efficient. In addition, lower sealingtemperatures may reduce the risk of thermal deformation or distortion ofthe packaging material, resulting in more attractive pouch appearance onthe store shelf.

A typical packaging pouch is a laminate of several films, typicallyconstructed of: A film that can be printed for the marketing of the foodproduct; a barrier film to inhibit the diffusion of oxygen and moistureand thus prolong the shelf-life of the product; and a sealant film whichprovides hermetic seals that also help prevent ingress of gases ormicrobes that could shorten the shelf-life of the product or causespoilage. In some cases, the barrier film and the sealant film can becombined into a single film that provides both functions of gas barrieras well as sealability. Typically, this sealant film is a non-oriented,cast polypropylene or polyethylene-based film. The polyethylene film canalso be made via blown film processes well-known in the art.

However, the high seal strengths required for some pouch packaging alsomake it difficult for the consumer to open the pouch by hand, especiallyif the retort package is made of all-polymeric films. Scissors or sharpimplements must typically be used to open such pouches. To make thepouches more user-friendly, notches can be used to enable the consumerto easily initiate a tear and thus open the pouch. However, such a tearcan easily result in “zippering” of the pouch whereby the tear is notuniformly parallel to the top edge of the pouch but can become verticalor diagonal to the top of the pouch and cause a potential loss orspillage of the contents during opening. To rectify this, some solutionsinvolve perforating a tear-line with the notch in order to keep the teardirectionally parallel to the top of the pouch and thus preventzippering. These perforations are often accomplished using mechanicalperforators or lasers. Some concerns using perforation techniques arenot only additional cost, but also the potential compromising of barrierproperties since these techniques are essentially making physical holesin the pouch laminate.

Another method to impart directional tear properties could be to orientthe cast polypropylene film typically used in pouch applications.However, the process of orienting such a film—either uniaxially orbiaxially—typically diminishes the seal properties in that the sealinitiation temperature (SIT) of the film is raised and the overall sealstrengths are weaker. Without being bound by any theory, this isbelieved to be due to the fact that the orientation process aligns theamorphous regions into a more ordered configuration, raising the Tg ofthe film, and thus, resulting in poorer seal properties. This is whyunoriented cast polypropylene works well as a sealant film versus, forexample, biaxially oriented polypropylene film (BOPP) which generallyfunctions poorly as a sealant film. (This is assuming that no coextrudedhighly amorphous/low crystallinity random copolymer heat sealable resinsare used as part of the BOPP film.) There is typically a minimum andmaximum range for uni-axial orientation stretching in the machinedirection (MDX): under 2.0 MDX, the film usually suffers from unevenstretching mark defects and over 7.0 MDX, processing stability can bedifficult to maintain, as the film may be prone to breakage at this highorientation rate.

Although crystalline propylene homopolymer and blends of crystallinepropylene homopolymer with impact ethylene-propylene copolymers willdisplay acceptable linear tear properties when oriented sufficiently inone direction, the higher content comonomer polypropylenes generally donot show acceptable linear tear properties by themselves. The reason forthe use of copolymer and terpolymers is to get acceptably low sealinitiation temperatures. Low seal initiation temperatures allow forfaster sealing speeds and use of certain lamination films that may meltor deform if too high a sealing temperature is used. Sealing films madewith crystalline propylene homopolymers as a component of the film,however, often show a higher-than-desired SIT and adjustments to raisesealer jaw temperature settings and/or to lower packaging machinelinespeeds to accommodate such homopolymer-containing sealing films areoften needed. Although such homopolymer-containing films can demonstrateexcellent directional or linear tear properties with an amount ofmono-orientation, SIT is often higher than desired. Although propylenecopolymers can demonstrate excellent SIT, they often fail to exhibitsatisfactory directional or linear tear properties when mono-oriented.

U.S. application Ser. No. 12/542,385 describes a linear or directionaltear retortable sealant film using blends of metallocene-catalyzedpropylene-butene elastomers and ethylene-propylene impact copolymerswhich are monoaxially oriented at least 4 times in the machinedirection. Typical seal initiation temperatures reported are about 320°F. (160° C.) or higher. This reference is incorporated herein in itsentirety.

U.S. patent RE30,726 describes a film including blended low densitypolyethylene and ionomer resins which is blow-extruded to form a filmwith linear tear properties in the direction of the extrusion.

U.S. Pat. No. 4,781,294 describes a tear-oriented package with one wallformed from foamed polypropylene and another from tear resistantpolyester film or another such substance. However, zones of weakening,such as perforations, are used to provide easy opening of the packaging.

U.S. Pat. No. 6,248,442 describes the use of a multilayered film thatincludes a layer of LLDPE which is biaxially oriented through theprocess of machine direction orientation. This produces a bag which canbe torn unidirectionally and which contains a resealable zipper.

U.S. Pat. No. 6,601,370 describes a process for forming a reclosablefilm package with a straight tear by attaching a nylon or polyesterlayer to a sealant layer, such as polyethylene. This involves two layersof overlapping films which propagate a tear along a linear path whensufficient force is applied.

U.S. Pat. No. 6,939,919 describes a blend of polypropylene andpolyethylene with enhanced properties, of which a majority ispolyethylene with a minority of the blend being polypropylene. However,this patent does not cite any linear tear properties of the resultantblend.

U.S. Pat. No. 6,541,086 describes a retort package design using anoriented polymer outer film (suitable for printing), an aluminum foil asa barrier film, a second oriented intermediate polymeric film, and anon-oriented polyolefin for the sealant film. Easy-tear functionality isadded by surface-roughening the two oriented polymer films andoverlapping them in a particular formation. The particular specificorder of laminating the films and the surface-roughening by sandpaperprovides for easy-tear properties and presumably directional tear, butthis process involves additional films and extra steps to accomplish thedesired tear properties.

U.S. Pat. No. 6,719,678 B1 describes a retort package design usingmultiple film layers whereby the intermediate layers (“burst resistantlayer”) are scored by a laser such that the score lines provide aneasy-tear feature and a directional tear feature.

U.S. Pat. No. 4,903,841 describes a retort package design that utilizesnon-oriented cast polypropylene films as the sealable layer, which issurface-roughened or scored in a particular manner so as to impartdirectional tear properties.

U.S. Pat. No. 4,291,085 describes a retort package design using anon-drawn, non-oriented cast crystalline polypropylene film as thesealable layer with specific crystalline structure and orientation ofthe crystalline structures which must be less than 3.0. There are nodirectional tear properties cited.

U.S. Pat. No. 5,786,050 describes an “easy opening” pouch design whichhas as the inner ply (which contacts the pouch's contents) a sealantfilm including linear low density polyethylene; an intermediate layercomposed of an oriented polyolefin with an MD/TD ratio of greater than2; and an outermost layer of biaxially oriented PET or nylon film. Theinner ply sealant of linear low density polyethylene is non-oriented.The specific orientation ratios of the intermediate film impartseasy-tear properties.

U.S. Pat. No. 4,834,245 describes a pouch design having a “tearing zone”using a monoaxially oriented film with a pair of notches aligned withthe tearing direction and the direction of orientation of the film. Themonoaxially oriented film that imparts the “tearing zone” is on theoutside of the pouch and does not contact the pouch contents and is notdesigned or considered to be appropriate for heat-sealability.

U.S. patent application Ser. No. 11/596,776 describes a pouch designincluding at least one uni-directionally stretched film. The preferredembodiments describe a uni-directionally stretched polypropylene film oruni-directionally stretched polyethylene terephthalate film whichimparts the easy-tear property. The application is silent as to thesealing properties of these layers or even which layer should be thesealant film.

SUMMARY OF THE INVENTION

The above issues of making a heat sealable film with excellent sealingcharacteristics such as a low seal initiation temperature with excellentlinear tear properties without using mechanical or laser perforationschemes or surface roughening and/or scoring methods are addressed. Theinventors have found a blend that balances these attributes for lineartear with a low seal initiation temperature. The linear tear propertyand low SIT is enhanced via the addition of about 3 to 65 wt % of lowdensity polyethylene (LDPE) with about 97 to 35 wt % of a propylenerandom copolymer. The LDPE has a degree of incompatibility with thepropylene-based copolymers and, when oriented in one direction, thisincompatible blend exhibits excellent linear tear properties. Thedirectional tear property is imparted via machine direction (MD)orientation of the cast film from about 2.5 times to 7 times originallength. This combination of MD orientation and resin formulationprovides excellent directional tear properties without compromising thehigh seal strength and hermetic seal properties required for pouches.

One embodiment is a monoaxially oriented film including a single layer(A) of a propylene random copolymer blended with an amount of lowdensity polyethylene homopolymer (LDPE). This layer (A) formulation issuitable for heat sealable applications, particularly for packagingapplications. Another embodiment could include a laminate film in whicha second polyolefin resin-containing layer (B) could be coextruded onone side of the layer (A). This second polyolefin resin-containing layercould be considered a core or base layer to provide the bulk strength ofthe laminate film. Preferably, this core layer (B) could also include anethylene-propylene impact copolymer. Furthermore, in another embodiment,the laminate could further include a third polyolefin resin-containinglayer (C) on the second polyolefin resin-containing core layer (B)opposite the side with the heat sealable layer (A).

Preferably, the heat sealable layer (A) includes a majority component ofa propylene random copolymer. The propylene-based random copolymer maybe a copolymer of propylene with ethylene, butene, or combinations ofboth (i.e. ethylene-propylene-butene copolymer). The propylene-basedrandom copolymer may be catalyzed via Zieglar-Natta or by metalloceneprocesses. The propylene-based random copolymer may be a highermolecular weight copolymer (e.g. ca. 350,000 M_(w), or higher) or alower molecular weight one such as an elastomer or plastomer (e.g. lessthan 350,000 M_(w), or about 5000-100,000 M_(w)). The other component ofthis blend is the addition of an amount of low density polyethylene.Typically, the LDPE is a minority component, including about 3-30 wt %of the layer (A), but it can include up to 65 wt % of the layer (A).

This heat sealable propylene copolymer/LDPE resin-containing layer (A)can also optionally include an antiblock component selected from thegroup consisting of amorphous silicas, aluminosilicates, sodium calciumaluminum silicates, glass microspheres, talcs, micas, minerals,crosslinked silicone polymers, and polymethylmethacrylates to aid inmachinability and winding. It can also be contemplated todischarge-treat one side of the layer (A) in order to enhance that sidefor laminating via adhesives, etc. Discharge-treating can be done by anyof several means well known in the art, such as corona, flame, plasma,or discharge-treatment in a controlled atmosphere of selected gases.

This film layer (A) is then monoaxially oriented from about 2.5-7 timesin the machine direction, preferably 3-7 times, and more preferably 4.0to 6.0 times. This monoaxial orientation imparts a directional tearproperty to the film. The resin formulation of the (A)-layer providesexcellent seal initiation, seal strengths, and hermetic seal propertiesafter monoaxial orientation, suitable for many pouch applications.

In the embodiment of a 2-layer laminate film structure, the (A)-layercould include a sealant layer on one side of a core layer (B).Preferably, this core layer (B) includes a polyolefin resin-containinglayer which in turn, includes a propylene homopolymer or propylenecopolymer. More preferable is an ethylene-propylene impact copolymer.The (A)-layer can be the same thickness as the (B) core layer, butpreferably is thinner than the (B)-layer, about 5-50% of the totalthickness of the (A) and (B) layers combined, more preferably 10-30% ofthe total thickness of the laminate film structure (A) and (B) layerscombined. This core polyolefin resin-containing layer can also includean antiblock component selected from the group consisting of amorphoussilicas, aluminosilicates, sodium calcium aluminum silicates, glassmicrospheres, talcs, micas, minerals, crosslinked silicone polymers, andpolymethylmethacrylates to aid in machinability and winding. It can alsobe contemplated to discharge-treat the side of the core layer (B)opposite the heat sealable layer (A) in order to enhance that side forlaminating via adhesives, etc. Discharge-treating can be done by any ofseveral means well known in the art, such as corona, flame, plasma, ordischarge-treatment in a controlled atmosphere of selected gases.

In the embodiment of a 3-layer laminate film structure, a third layer(C) could be disposed on the side of the core layer (B) opposite theheat sealable layer (A) and preferably includes a polyolefinresin-containing layer which in turn, includes a polyolefin selectedfrom the group consisting of propylene homopolymer, copolymers,terpolymers, polyethylene, maleic anhydride-grafted polyolefins, andcombinations thereof. This third polyolefin resin-containing layer canalso include an antiblock component selected from the group consistingof amorphous silicas, aluminosilicates, sodium calcium aluminumsilicates, glass microspheres, talcs, micas, minerals, crosslinkedsilicone polymers, and polymethylmethacrylates to aid in machinabilityand winding. The third polyolefin layer can also be a discharge-treatedlayer having a surface for lamination, metallizing, printing, or coatingwith adhesives or inks as described previously.

In the case of a film structure including only one layer, such as theheat sealable layer (A), as mentioned previously, it can be contemplatedto discharge-treat one side of this layer for lamination, metallizing,printing, or coating, while leaving the opposite side untreated in orderto maintain heat sealable properties. Discharge-treating this layer canresult in the treated side having a narrower seal range due tocrosslinking of the ethylene and/or butene constituents of the blend.Thus, at least one side should be left untreated in order to obtain thefull and useful heat seal range. In the case of a 2-layer (or more)laminate structure wherein the sealable layer (A) is contiguous with apolyolefin core layer (B), it is preferable to discharge-treat the sideof the core layer opposite the sealable layer (A) for purposes oflaminating, printing, metallizing, coating, etc.

Discharge-treatment in the above embodiments can be accomplished byseveral means, including but not limited to corona, flame, plasma, orcorona in a controlled atmosphere of selected gases. Preferably, in onevariation, the discharge-treated surface has a corona discharge-treatedsurface formed in an atmosphere of CO₂ and N₂ to the exclusion of O₂.The laminate film embodiments could further include a vacuum-depositedmetal layer on the discharge-treated layer's surface. Preferably, themetal layer has a thickness of about 5 to 100 nm, has an optical densityof about 1.5 to 5.0, and includes aluminum. In one variation, thelaminate film is an extruded laminate film.

In yet another embodiment, this invention provides monoaxially orientedpolyolefin films with a heat sealable layer of blends of propylenerandom copolymers, elastomers, and plastomers with low densitypolyethylene to enhance heat sealing properties for flexible packagingpurposes. An additional embodiment provides laminate structures of theheat sealable polyolefin blend layers for heat sealable applications inflexible packaging.

Preferably, the monoaxially oriented film is produced via extrusion ofthe heat sealable layer blend through a die whereupon the molten filmlayer is quenched upon a chilled casting roll system or casting roll andwater bath system and subsequently oriented in the machine direction andannealed or heat-set to minimize thermal shrinkage into a thermally,dimensionally stable film.

In the embodiments of a multi-layer film, the laminate film is producedvia coextrusion of the heat sealable layer blend and the core layerand/or other layers through a compositing die whereupon the moltenmultilayer film structure is quenched upon a chilled casting roll systemor casting roll and water bath system and subsequently oriented in themachine direction and annealed or heat-set into a multi-layer film.

All these examples can also be metallized via vapor-deposition,preferably a vapor-deposited aluminum layer, with an optical density ofat least about 1.5, preferably with an optical density of about 2.0 to4.0, and even more preferably between 2.3 and 3.2. In the embodiments inwhich the invention is part of a multi-layer coextruded film, the metalreceiving layer or surface may be specially formulated ordischarge-treated to enhance metal deposition, metal nucleation, andmetal adhesion properties.

This invention provides a method to improve the heat sealability ofmonoaxially oriented films resulting in an economical, highly sealablefilm with excellent directional tear properties suitable for packagingapplications. The invention helps solve the problems associated with theprior art of directional tear polyolefin substrates in packagingapplications.

Additional advantages of this invention will become readily apparent tothose skilled in the art from the following detailed description,wherein only the preferred embodiments of this invention is shown anddescribed, simply by way of illustration of the best mode contemplatedfor carrying out this invention. As will be realized, this invention iscapable of other and different embodiments, and its details are capableof modifications in various obvious respects, all without departing fromthis invention. Accordingly, the examples and description are to beregarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE INVENTION

Described are mono-oriented films that possess linear tear properties.The films include a blend of an incompatible polymer such as low densitypolyethylene (LDPE) with propylene-based random copolymers and/orterpolymers. The films, when mono-oriented, display the tendency tofibrillate. These properties, for example, facilitate a linear tear in apouch made utilizing the films layer. Neither LDPE nor the highermodified polypropylene polymers will display the linear tear propertiesalone, even when mono-oriented.

When mono-oriented, homopolymer and impact propylene-based resins willdisplay linear or directional tear properties without furthermodification. Described are formulations that provide a linear tear filmwith lower melting temperature polymers. This allows for a heat seallayer film with significantly lower seal initiation temperature thatstill retains linear tear properties.

In some embodiments, the films are well-suited as the sealable filmcomponent for certain pouch packaging applications, in particular,non-retortable pouches. In addition, the films are highly suitable forpackages that require hand-tearability and can produce a tear line thatis controlled and consistent across the top of the pouch and parallel tothe top of the pouch, without causing “zippering” of the pouch andsubsequent potential loss of the contents. This invention is novel inthat it combines both excellent seal strengths and hermetic sealssuitable for pouching and directional tear, obviating the need forperforation techniques to enable directional tear.

In one embodiment, the laminate film includes a single-layermono-oriented extruded film of: A mixed polyolefin resin layer includinga propylene random copolymer and an amount of a low density ethylenehomopolymer. Another embodiment of the inventive film includes a similarformulation as above, except that one side of the mixed polyolefin resinlayer is discharge-treated.

The mixed polyolefin resin layer is uniaxially oriented. The propylenerandom copolymer can be an isotactic ethylene-propylene impact copolymerwith an ethylene-propylene rubber content of about 10-30 wt % of thepolymer wherein the ethylene content of the rubber is about 10-80 wt %of the rubber. Typically, the copolymer is an ethylene-propylenecopolymer, an ethylene-butene copolymer, a propylene-butene copolymer,or an ethylene-propylene-butene copolymer. Preferably, anethylene-propylene or ethylene-propylene-butene copolymer is used. Thecopolymer may be an elastomer or plastomer. A thermoplastic elastomercan be described as any of a family of polymers or polymer blends (e.g.plastic and rubber mixtures) that resemble elastomers in that they arehighly resilient and can be repeatably stretched and, upon removal ofstress, return to close to its original shape; is melt-processable at anelevated temperature (uncrosslinked); and does not exhibit significantcreep properties. Thermoplastic elastomers typically have a density ofbetween 0.860 and 0.890 g/cm³ and a molecular weight M_(w), of 100,000or greater. Plastomers differ from elastomers: a plastomer can bedefined as any of a family of ethylene-based copolymers (i.e. ethylenealpha-olefin copolymer) which has properties generally intermediate tothose of thermoplastic materials and elastomeric materials (thus, theterm “plastomer”) with a density of less than about 0.900 g/cm³ (down toabout 0.865 g/cm³) at a molecular weight M_(w) between about 5000 and50,000, typically about 20,000 to 30,000. Plastomers generally have anethylene crystallinity between thermoplastics and ethylene alpha-olefinelastomers and are generally of a higher crystallinity than elastomers(which can generally be considered amorphous). As such, plastomersgenerally have better tensile properties than elastomers.

A suitable example of ethylene-propylene impact copolymer for is TotalPetrochemical's 5571. This resin has a melt flow rate of about 7 g/10minutes at 230° C., a melting point of about 160-165° C., a Vicatsoftening point of about 148° C., and a density of about 0.905 g/cm³.Another example of ethylene-propylene impact copolymer can be TotalPetrochemical's 4180 with a melt flow rate of about 0.7 g/10 minutes at230° C., a melting point of about 160-165° C., a Vicat softening pointof about 150° C., and a density of about 0.905 g/cm³. Other suitableethylene-propylene impact copolymers can be Sunoco Chemical's TI-4015-Fwith a melt flow rate of 1.6 g/10 minutes at 230° C. and a density ofabout 0.901 g/cm³ and ExxonMobil Chemical's PP7033E2 with a melt flowrate of about 8 g/10 minutes at 230° C. and a density of about 0.9g/cm³.

Suitable examples of propylene random copolymers are: TotalPetrochemicals Z9421 ethylene-propylene random copolymer elastomer ofabout 5.0 g/10 min melt flow rate (MFR) at 230° C., melting point ofabout 120° C., density 0.89 g/cm³, and ethylene content of about 7 wt %of the polymer; Total Petrochemicals 8473 ethylene-propylene randomcopolymer of about 4.0 MFR at 230° C. and ethylene content of about 4.5wt % of the polymer; Sumitomo Chemical SPX78R1 ethylene-propylene-butenerandom copolymer of about 9.5 g/10 min MFR at 230° C., ethylene contentof about 1.5 wt %, and butene content of about 16 wt % of the polymer;or ExxonMobil Chemical Vistamaxx™ ethylene-propylene random copolymerelastomers such as grade 3980 FL with an MFR of about 8.3 g/10 min at230° C., Vicat softening point of about 80° C., melting point of about79° C., density of about 0.879 g/cm³, and ethylene content of about 8.5wt %. Other suitable propylene-based copolymers and elastomers may becontemplated including but not limited to: metallocene-catalyzedthermoplastic elastomers like ExxonMobil's Vistamaxx™ 3000 grade, whichis an ethylene-propylene elastomer of about 11 wt % ethylene content, 8g/10 min MFR at 230° C., density of 0.871 g/cm³, T_(g) of −20 to −30°C., and Vicat softening point of 64° C.; or ethylene-propylenealpha-olefin copolymer plastomers of Dow Chemical's Versify™ grades,such as grade 3300, which is an ethylene-propylene plastomer of about 12wt % ethylene content, 8 g/10 min MFR at 230° C., density of 0.866g/cm³, T_(g) of −28° C., and Vicat softening point of 29° C.

A suitable example of LDPE is ExxonMobil LD105.30 low density ethylenehomopolymer resin of about 2.0 g/10 min melt flow index at 190° C.,melting point about 111° C., and density of about 0.923 g/cm³. Othergrades of LDPE of similar properties can be used as well and theinvention is not limited to only the grades described.

The LDPE is blended with the propylene-based random copolymer at about 3to 65 wt % of the layer, preferably about 5-50 wt %, and more preferablyabout 10-40 wt %. A higher content of LDPE (e.g. 40-65 wt %) helpsimprove the inventive film's bonding to polyethylene-based zipper stockscommonly used in pouching applications; however, optical clarity may beworsened by the higher loadings. Optionally, whitening pigments can beadded to the inventive film to produce a white sealant film, useful forcertain aesthetic appearance to the pouch or package application.Whitening agents can include—but are not limited to—TiO₂, bariumsulfates, optical brighteners, or calcium carbonates.

It can also be contemplated to add an optional amount of antiblockingagent to the mixed resin film layer for aiding machinability andwinding. An amount of an inorganic antiblock agent can be added in theamount of 100-5,000 ppm of the heat sealable resin layer (A), preferably500-1000 ppm. Preferred types of antiblock are spherical sodium aluminumcalcium silicates or an amorphous silica of nominal 6 μm averageparticle diameter, but other suitable spherical inorganic antiblocks canbe used including crosslinked silicone polymer orpolymethylmethacrylate, and ranging in size from 2 μm to 6 μM. Migratoryslip agents such as fatty amides and/or silicone oils can also beoptionally employed in the film layer either with or without theinorganic antiblocking additives to aid further with controllingcoefficient of friction and web handling issues. Suitable types of fattyamides are those such as stearamide or erucamide and similar types, inamounts of 100-5000 ppm of the layer. Preferably, erucamide is used at500-1000 ppm of the layer. A suitable silicone oil that can be used is alow molecular weight oil of 350 centistokes which blooms to the surfacereadily at a loading of 400-600 ppm of the layer. However, if the filmsare desired to be used for metallizing or high definition processprinting, it is recommended that the use of migratory slip additives beavoided in order to maintain metallized barrier properties and adhesionor to maintain high printing quality in terms of ink adhesion andreduced ink dot gain.

This mixed resin layer (A) of propylene-based random copolymer and LDPEis typically 50 μm to 200 μm in thickness after monoaxial orientation,preferably between 60 μm and 150 μm, and more preferably between 70 μmand 100 μm in thickness. The mixed resin layer can also be surfacetreated on one side with either an electrical corona-discharge treatmentmethod, flame treatment, atmospheric plasma, or corona discharge in acontrolled atmosphere of nitrogen, carbon dioxide, or a mixture thereof,with oxygen excluded and its presence minimized. The latter method ofcorona treatment in a controlled atmosphere of a mixture of nitrogen andcarbon dioxide results in a treated surface that includesnitrogen-bearing functional groups, preferably at least 0.3 atomic % ormore, and more preferably, at least 0.5 atomic % or more. Thedischarge-treated mixed resin layer is then well suited for subsequentpurposes of laminating, coating, printing, or metallizing.

In the embodiments in which a multi-layer film such as a two-layerlaminate film or a three-layer laminate film is contemplated, the mixedresin layer (A) of the previously described propylene random copolymerand LDPE can be coextruded with another layer. In the embodiment of a2-layer laminate film structure, the mixed resin layer (A) includes asealant layer on one side of a core layer (B). Preferably, this corelayer (B) includes a polyolefin resin-containing layer which in turn,includes a propylene homopolymer or propylene copolymer. More preferableis an ethylene-propylene impact copolymer or an ethylene-propylenerandom copolymer of similar types used as a component of the (A)-layersuch as the previously described Total 5571 isotactic ethylene-propyleneimpact copolymer or other copolymer grades mentioned. The (A)-layer canbe the same thickness as the (B) core layer, but preferably is thinnerthan the (B)-layer, about 5-50% of the total thickness of the (A) and(B) layers combined, more preferably 10-30% of the total thickness ofthe laminate film structure (A) and (B) layers combined. This corepolyolefin resin-containing layer can also include an antiblockcomponent selected from the group consisting of amorphous silicas,aluminosilicates, sodium calcium aluminum silicates, crosslinkedsilicone polymers, and polymethylmethacrylates to aid in machinabilityand winding. Migratory slip additives such as fatty amides or siliconeoils could also be added as previously described if desired. It can alsobe contemplated to discharge-treat the side of the core layer (B)opposite the heat sealable layer (A) in order to enhance that side forlaminating via adhesives, etc. Discharge-treating can be done by any ofseveral means well known in the art, such as corona, flame, plasma, ordischarge-treatment in a controlled atmosphere of selected gases asdescribed previously.

In the embodiment of a 3-layer laminate film structure, a third layer(C) would be disposed on the side of the core layer (B) opposite theheat sealable mixed resin layer (A) and preferably includes a polyolefinresin-containing layer which in turn, includes a polyolefin selectedfrom the group consisting of propylene homopolymer, copolymers,terpolymers, polyethylene, or maleic anhydride-grafted polypropylene,polyethylene, or copolymers thereof, and combinations of all thereof.This third layer (C) will generally be thinner than the core layer (B)and can be a thickness ranging 2-30% of the combined thickness of the 3layers together, perferably about 5-10% of the overall thickness of themulti-layer laminate. This third polyolefin resin-containing layer canalso include an antiblock component selected from the group consistingof amorphous silicas, aluminosilicates, sodium calcium aluminumsilicates, crosslinked silicone polymers, and polymethylmethacrylates toaid in machinability and winding and/or migratory slip additives such asfatty amides or silicone oils. The third polyolefin layer can also be adischarge-treated layer having a surface for lamination, metallizing,printing, or coating with adhesives or other materials.

In the above embodiments of multi-layer films, the respective layers canbe coextruded through a multi-layer compositing die such as a 2- or3-layer die, and cast onto a chill roll to form a solid film suitablefor further processing. In the case of a single layer film, therespective layer can be extruded through a single-layer die and castonto a chill roll to form a solid film suitable for further processing.Extrusion temperatures are typically set at 235-270° C. with a resultingmelt temperature at the die of about 230-250° C.

In all these embodiments, a key element is to monoaxially orient thefilm layer in the machine direction to a certain amount. It is thismonoaxial orientation that imparts the directional or linear tearingproperties that make it useful in pouching applications. It is thecombination of this monoaxial orientation with the heat sealable resinformulation of propylene-based random copolymer and low densitypolyethylene that allows excellent and suitable heat seal initiation andseal strengths fit-for-use in pouch applications and excellentdirectional and linear tear properties. The amount of monoaxial machinedirection orientation should be about 2.5-7 times in the machinedirection, preferably 3-7 times, and more preferably 4.0 to 6.0 times.Suitably clean and linear tear properties are found at these monoaxialorientation rates. However, above a 7:1 machine direction orientationratio, processability issues may result such as film breakage which canaffect the product cost and machine efficiency; below a 2.5:1 machinedirection orientation ratio, processability issues such as uneven filmprofile, gauge bands, and uneven stretch marks can occur which also canresult in higher product costs and lower machine efficiencies.

Surprisingly, it is the combination of the propylene random copolymer,LDPE, and MD orientation as described above, that provides bothexcellent SIT and directional tear properties. MD orientation of each ofthe resin components alone—i.e. the unblended propylene random copolymeror the unblended LDPE—does not provide satisfactory directional tear.Without being bound by any theory, it is hypothesized that theincompatibility of the LDPE in the propylene-based random copolymerduring mono-orientation aids in forming “fibrils” which improves thedirectional or linear tear properties. It is believed that the domainsor regions of incompatible LDPE within the propylene-based copolymermatrix become oriented or ordered during mono-orientation in such a waythat these “oriented domains” form zones or “fault lines” thatfacilitate linear tear parallel to the direction of orientation. It isnoted that mono-orientation of propylene-based random copolymers or LDPEby itself did not exhibit satisfactory linear tear (although incontrast, mono-orientation of high density polyethylene (HDPE) doesexhibit good linear tear properties; it is possible that the orientationof the crystalline and amorphous regions in the HDPE provide good lineartear properties).

Indeed, it is possible that any incompatible polymer to thepropylene-based random copolymer could help improve linear tearproperties of amorphous or low crystallinity mono-oriented polymerfilms. It can also be speculated that the principle could be applied tocast or blown LDPE films whereby an incompatible polymer (e.g. propylenerandom copolymer or homopolymer) is added as a minority component to theLDPE film, oriented in machine direction, and thus exhibit satisfactorylinear tear properties as well as low seal initiation properties similarto conventional blown or cast LDPE films used as heat sealing films.

Moreover, the limited compatibility of the LDPE with the ethyleneportions of the propylene random copolymer also helps maintain desirableoptical clarity properties (reduced haze if transparent film is desired)and significantly lower seal initiation temperatures. With higherloadings of LDPE, the directional tear properties are seen to begenerally further improved (with a fixed mono-orientation rate) as wellas heat seal initiation temperature; while heat seal properties forstrength and hot tack are maintained by the propylene-based randomcopolymers.

The inventive resin blend—whether in single layer or multi-layerembodiments—is extruded into a sheet form and cast onto a cooling drumat a speed of 6 to 15 mpm whose surface temperature is controlledbetween 20° C. and 60° C. to solidify the non-oriented laminate sheet.The non-oriented laminate sheet is stretched in the longitudinaldirection at about 90° C. to 110° C. at a stretching ratio of about 2.5to about 7 times the original length, and most preferably between about4.0 and 6 times, and the resulting stretched sheet is annealed orheat-set at about 130° C. to 150° C. in the final zones of the machinedirection orientation section to reduce internal stresses and minimizethermal shrinkage and to obtain a dimensionally stable uniaxiallyoriented laminate sheet. After orientation, the typical film thicknessis 50-200 μm and most preferably, 70-100 μm. The uniaxially orientedsheet can then pass through a discharge-treatment process on one side ofthe film such as an electrical corona discharge treater to impart asuitable surface for lamination to other films as desired. The one-sidetreated film is then wound into roll form.

A further embodiment is to metallize the discharge-treated surface ofthe resin blend layer. The unmetallized laminate sheet is first wound ina roll. The roll is placed in a metallizing chamber and the metalvapor-deposited on the discharge-treated mixed resin metal receivinglayer surface. The metal film may include titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, zinc, aluminum, gold, orpalladium, the preferred being aluminum. Metal oxides—as well as siliconoxides—can also be contemplated, the preferred being aluminum oxide. Themetal layer can have a thickness between 5 and 100 nm, preferablybetween 20 and 80 nm, more preferably between 30 and 60 nm; and anoptical density between 1.5 and 5.0, preferably between 2.0 and 4.0,more preferably between 2.3 and 3.2. The metallized film is then testedfor oxygen and moisture gas permeability, optical density, metaladhesion, metal appearance and gloss, and can be made into an adhesivelaminate structure.

An additional embodiment can be contemplated in which the inventive filmformulation can be co-extruded or coated with a polymeric or organic gasbarrier material upon one side of the film. Preferably, a barriercoating can be applied to the discharge-treated surface or side of theinventive film. Such barrier coatings can include, but are not limitedto, polyvinyl alcohol, ethylene vinyl alcohol, polyhydroxyaminoether,polyvinylidene chloride, vinyl alcohol-vinyl amine, or blends thereof,and either crosslinked or uncrosslinked. Such coatings may also requirethe use of a primer layer or tie-layer either coated onto the inventivefilm prior to the application of the barrier layer in order to providestrong bonds between the inventive film layer and the barrier layers; orco-extruded as a skin layer with the inventive film layer or blendedinto the inventive film layer as an optional component. A suitabletie-layer or tie-resin for blending can include a maleicanhydride-grafted polyolefin. The barrier coatings may be applied ineither off-line or in-line coating processes well known in the art. Itcan also be contemplated to coextrude the barrier layer using (but notlimited to) extrusion-grade ethylene vinyl alcohol resin, polyvinylalcohol resin, or polyhydroxyaminoether resin. Again, a tie-layer may beadvantageously coextruded as an intermediate layer between the barrierlayer and the inventive film layer to improve bonding of these polar andnon-polar polymers. A preferred embodiment would be to further metallizeas described previously upon the surface of the barrier layer which isopposite the side with the inventive film layer.

This invention will be better understood with reference to the followingexamples, which are intended to illustrate specific embodiments withinthe overall scope of the invention.

Example 1

A single layer monoaxially oriented film was made using a monoaxialorientation process, including a blend of about 97 wt % Total Z9421ethylene-propylene random copolymer and about 3 wt % ExxonMobil LD105.30 low density polyethylene with about 1 part per hundred (phr)concentration of Ampacet 40878 Skiblock™ 5 wt % synthetic silica(nominal 2.0 μm size) antiblock masterbatch in propylene homopolymercarrier resin. The resin mixture was pellet-blended, then melt-extrudedthrough a die, cast on a chill drum, and oriented in the machinedirection at a 4.8:1.0 stretch ratio, through a series of heated anddifferentially sped rolls. The film was heat-set or annealed in thefinal zones of the MD orientation section to reduce internal stressesand minimize heat shrinkage of the film and maintain a dimensionallystable monoaxially oriented film. Final film thickness after orientationwas ca. 70 μm (280G). One surface of the film (the cast roll side) istreated via discharge treatment methods such as corona or flame or othermethods, after orientation, in order to provide a higher surface energy,functionalized surface for further adhesive or extrusion lamination,coating, printing, or metallizing. The opposite side (air side ornon-cast roll side) of the film is left untreated in order to preservethe heat sealable properties of the film. The mono-oriented film waswound in roll form and tested for haze, heat sealability, sealinitiation temperature, and directional tear.

Example 2

Example 1 was substantially repeated except that the mixed resin layerwas changed to a blend of about 90 wt % Z9421 random copolymer and about10 wt % LD105.30 LDPE. About 1 part per hundred (phr) concentration ofAmpacet 40878 synthetic silica antiblock masterbatch was added.

Example 3

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 40 wt % Z9421 random copolymer, about 40 wt %Vistamaxx™ 3980 elastomer, and about 20 wt % LD105.30 LDPE. About 4.6parts per hundred (phr) concentration of Ampacet 40878 synthetic silicaantiblock masterbatch was added.

Example 4

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 80 wt % Vistamaxx™ 3980 elastomer and about 20 wt %LD105.30 LDPE. About 4.6 parts per hundred (phr) concentration ofAmpacet 40878 synthetic silica antiblock masterbatch was added.

Example 5

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 40 wt % Vistamaxx™ 3980 elastomer, about 40 wt %Sumitomo SPX78R1 ethylene-propylene-butene copolymer, and about 20 wt %LD105.30 LDPE. About 2 parts per hundred (phr) concentration of Ampacet40878 synthetic silica antiblock masterbatch was added.

Example 6

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 45 wt % Vistamaxx™ 3980 elastomer, about 30 wt %Sumitomo SPX78R1 ethylene-propylene-butene copolymer, and about 25 wt %LD105.30 LDPE. About 2 parts per hundred (phr) concentration of Ampacet40878 synthetic silica antiblock masterbatch was added.

Example 7

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 35 wt % Vistamaxx™ 3980 elastomer and about 65 wt %LD105.30 LDPE. About 4 parts per hundred (phr) concentration of Ampacet40878 synthetic silica antiblock masterbatch was added.

Comparative Example 1

Example 1 was substantially repeated except that the mixed resin layerwas changed to 100 wt % Z9421 ethylene-propylene random copolymer. NoAmpacet 40878 synthetic silica antiblock masterbatch was added.

Comparative Example 2

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 85 wt % Z9421 random copolymer and about 15 wt %high crystalline propylene homopolymer (Total Petrochemical 3270, meltflow rate 2.0 g/10 min at 230° C., 165° C. melting point, 0.91 g/cm³density). About 1 part per hundred (phr) concentration of Ampacet 40878synthetic silica antiblock masterbatch was added.

Comparative Example 3

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 70 wt % Z9421 random copolymer and about 30 wt %high crystalline propylene homopolymer (Total Petrochemical 3270, meltflow rate 2.0 g/10 min at 230° C., 165° C. melting point, 0.91 g/cm³density). About 1 part per hundred (phr) concentration of Ampacet 40878synthetic silica antiblock masterbatch was added.

Comparative Example 4

Example 1 was substantially repeated except that the mixed resin layerwas changed to about 90 wt % Z9421 random copolymer and about 10 wt %cyclic olefin copolymer (Topas TO 9506F-04 cyclic olefin copolymer (COC)resin, 5.5 g/10 min MFR at 230° C., density 1.02 g/cm³, and a glasstransition temperature of 65° C.). About 1 part per hundred (phr)concentration of Ampacet 40878 synthetic silica antiblock masterbatchwas added.

The formulations and unlaminated properties of the Examples andComparative Examples (“CEx.”) are shown in Tables 1 and 2 respectively.

TABLE 1 Composition (wt % except as noted) CEx1 CEx 2 CEx 3 CEx 4 Ex 1Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Ex 7 Total Z9421 100 85 70 90 97 90 40 0 0 0 0ExxonMobil 3980 FL 0 0 0 0 0 0 40 80 40 45 35 Sumitomo SPX78R1 0 0 0 0 00 0 0 40 30 0 Total 3270 0 15 30 0 0 0 0 0 0 0 0 ExxonMobil LD105.30 0 00 0 3 10 20 20 20 25 65 Topas TO9506F-04 0 0 0 10 0 0 0 0 0 0 0 Ampacet40878 (phr) 0 1 1 1 1 1 4.6 4.6 2 2 4

TABLE 2 Tear Seal Initiation Heat Seal Heat Seal Rating TemperatureStrength Strength (1 = good; (SIT) ° F. @ 290° F. @143.3° C. Sample 4 =poor) Haze % (° C.) lbf/in N/25 mm CEx. 1 3 7.2 285 (140.6) 2.46 10.94CEx. 2 3 15.9 330 (165.6) N/A* N/A* CEx. 3 2 10.5 335 (168.3) N/A* N/A*CEx. 4 4 10.1 285 (140.6) 4.64 20.64 Ex. 1 2 6.95 285 (140.6) 8.02 35.67Ex. 2 1 6.6 280 (137.8) 9.03 40.17 Ex. 3 1 19.1 265 (129.4) 2.09  9.30Ex. 4 4 59.7 230 (110.0) 7.49 33.32 Ex. 5 1 30.3 230 (110.0) 5.68 25.27Ex. 6 1 39.4 250 (121.1) 3.59 15.97 Ex. 7 1 43.2 250 (121.1) 4.80 21.35*These examples did not record a value due to SIT being greater than290° F. (143.3° C.)

As Table 1 showed, Comparative Example 1 (CEx 1) was a film includingabout 100 wt % Total Z9421 ethylene-propylene random copolymer. Table 2shows test data for this composition having good haze of 7.2%. Any valueless than 30 percent would be good for a clear packaging application,with up to 60 percent being acceptable for translucent applications.This film also showed an acceptable SIT and marginal heat seal strengthof 2.46 lb_(f)/in (10.94 N/25 mm) at 290° F. (143.3° C.). However, whena film sheet was torn by hand at a notch along the machine direction,the appearance of the tear initiation point showed a qualitative 3rating with stress-whitening and deformation and the torn edge was foundto be irregular and often zippered down the face of the package in thetransverse direction. A tear property rating of 1 or 2 is desirable,which indicates good directional tear properties and no or littlezippering or non-uniform tear. CEx1's directional tear was considered tobe poor or marginal at best.

Comparative Example 2 (CEx 2) showed a film formulation that used 85 wt% Total Z9421 random copolymer and 15 wt % Total 3270 high crystallinepropylene homopolymer and which incorporated the Ampacet antiblock. Inthis example, the SIT was significantly higher than that of CEx 1 due tothe addition of crystalline propylene homopolymer. Haze remainedcomparable at 15.9. However, the directional tear was still poor.Although the film could be rapidly torn with a fairly straight-edge andparallel to the machine direction of the sheet, if the tear wasinterrupted it could be torn at an angle. The addition of thecrystalline homopolymer was to improve directional tear properties afterorientation; compared to CEx.1, directional tear was improved, thoughnot enough.

Comparative Example 3 (CEx. 3) showed a film formulation that uses 70 wt% Total Z9421 random copolymer and 30 wt % Total 3270 high crystallinepropylene homopolymer and which incorporated the Ampacet antiblock. Inthis example, the SIT was significantly higher than that of CEx. 1 andslightly higher than that of CEx. 2 due to the increased amount ofcrystalline propylene homopolymer. Haze remained very comparable.However, directional tear was improved and was considered acceptable,though SIT was undesirably higher at 335° F. (168.3° C.).

Comparative Example 4 (CEx 4) showed a film that used 90 wt % TotalZ9421 random copolymer and 10 wt % cyclic olefin copolymer (COC) andwhich incorporated the Ampacet antiblock. No linear tear properties wereobserved with this formulation, though seal strength and SIT wereacceptable.

Example 1 (Ex. 1) is a film that used about 97 wt % Total Z9421ethylene-propylene random copolymer and about 3 wt % LDPE and whichincorporated an amount of the Ampacet silica antiblock. This film showedan acceptable improvement in the tear properties from those of CEx. 1, 2and 4 in addition to significantly improved heat seal strength and anacceptable SIT.

Example 2 (Ex. 2) showed a film that used 90 wt % Total Z9421 randomcopolymer and 10 wt % LDPE and which incorporated the Ampacet antiblock.It had excellent tear properties with no loss of heat seal strength orSIT properties. The additional LDPE also improved the bonds to LDPEbased zipper stock, which is added to many packages to make themresealable. Directional tear was extremely good, with the tearpropagating cleanly from the notch with no stress-whitening ofdeformations. The tear itself was very straight edged and parallel tothe machine direction of the sheet.

Example 3 (Ex. 3) showed a film that used 40 wt % Total Z9421 randomcopolymer, 40 wt % Vistamaxx 1980 elastomer, and 20 wt % LDPE and whichincorporated the Ampacet antiblock. This blend was designed to heat sealat a lower temperature than the prior examples. The LDPE percentage wasincreased for even better heat seal bonds to the LDPE zipper stock. This20 wt % of LDPE formed acceptable 7 lb/in seals (31.14 N/25 mm) to thezipper stock. Tear properties were excellent. The haze was a bit higherand the seal strength was lower than that of prior examples.

Example 4 (Ex. 4) showed a film that used 80 wt % Vistamaxx 3980elastomer, and 20 wt % LDPE and which incorporated the Ampacetantiblock. This film did not incorporate enough LPDE to render lineartear properties to the film. The Vistamaxx was rather rubbery andoverwhelmed the 20 wt % LDPE part of the blend.

Example 5 (Ex. 5) showed a film that used 40 wt % Vistamaxx 3980elastomer, 40 wt % Sumitomo SPX78R random copolymer, and 20 wt % LDPEand which incorporated the Ampacet antiblock. It was fairly similar toExample 3, having excellent tear properties and also a lower SIT thanprior examples. The heat seal strength at 290° F. (143.3° C.) was higherthan that of Example 3, but not as high as that of Examples 1, 2, and 4.

Example 6 (Ex. 6) showed a film that used 45 wt % Vistamaxx 3980elastomer, 30 wt % Sumitomo SPX78R random copolymer, and 25 wt % LDPEand which incorporated Ampacet antiblock. This was a variation ofExample 5 and showed high haze but other properties were similar,including excellent tear properties.

Example 7 (Ex. 7) showed a film that was 35 wt % Vistamaxx 3980elastomer and 65 wt % LDPE with Ampacet antiblock master batch. The hazewas fairly high. It showed excellent tear properties, good heat sealstrength, and a low SIT due to the low melting point of the componentand the increased thickness of the film. This example's resultsindicates that it is possible that the minority component ofpropylene-based elastomer provided the incompatible “fibrils” for lineartear properties in the LDPE majority component.

Thus, the foregoing Examples show a way to maintain high seal strengths,low seal initiation temperatures, and yet provide the desirableattribute of directional tear that is imparted from orientationstretching of the film. Since it is expected that seal performance willbe worsened after orientation of the film, our invention unexpectedlyhas shown excellent seal performance with orientation of the film.

Test Methods

The various properties in the above examples were measured by thefollowing methods:

Heat seal strength: Measured by using a Sentinel sealer model 12 ASL at25 psi, 1.0 second dwell time, with heated flat upper seal jaw Tefloncoated, and unheated lower seal jaw, rubber with glass cloth covered.The film sample is heat-sealed to itself at the desired sealtemperature(s) in the Sentinel sealer (e.g. 310° F.). To prevent thefilm from sticking to the sealer's jaws, the test film can be laid ontoa heat-resistant film such as a biaxially oriented nylon orpolyethyllene terephthalate film (PET). These two films are then foldedover such that the nylon or PET film is outermost and in contact withthe heated sealer jaws; the test film is then the inner layer and willseal to itself upon application of heat and pressure. A 15-20 um thicknylon or PET film is recommended; if too thick, this may interfere withthermal transfer to the test film. The test film should be insertedbetween the heat sealer's jaws such that the film's machine direction isperpendicular to the heat sealer jaws. Heat seal temperatures may beincreased at desired intervals, e.g. 10° F. increments. The respectiveseal strengths are measured using an Instron model 4201 tensile tester.The heat-sealed film samples are cut into 1-inch wide strips along themachine direction; the two unsealed tails placed in the upper and lowerInstron clamps, and the sealed tail supported at a 90° angle to the twounsealed tails for a 90° T-peel test. The peak and average seal strengthis recorded. The preferred value is about 3 lb_(f)/in (13.35 N/25 mm) at290° F. (143.3° C.) seal temperature.

Seal initiation temperature: Heat seal initiation temperature (SIT) wasmeasured by using a Sentinel sealer model 12 ASL at 25 psi, 1.0 seconddwell time, with heated flat upper seal jaw Teflon coated, and unheatedlower seal jaw, rubber with glass-cloth covered. The film sample isheat-sealed to itself at various desired seal temperatures in theSentinel sealer and then the respective seal strengths are measuredusing an Instron model 4201 tensile tester as discussed above for heatseal strength determination. The Seal Initiation Temperature is definedas the seal temperature at which the film demonstrated a minimum of 1lb_(f)/in (4.45 N/15 mm) heat seal strength. The preferred SIT value is290° F. (143.3° C.) or lower.

Transparency of the film was measured by measuring haze of a singlesheet of film substantially in accordance with ASTM D1003. Preferredhaze value is 40% or less, though 60% haze or less can be acceptable forsome applications.

Directional tear is tested qualitatively by notching a piece of testfilm on the edge and tearing by hand at the notch to initiate the tear.The notch is made parallel to the machine direction and the tear will bepropagated along the machine direction. The tear is initiated from thenotch by hand and observation made as to whether any stress-whitening ordeformation occurs. As the tear is propagated, the consistency of thetorn edges and the angle at which the tear propagates is observed. Thepreferred observation for good directional tear property is: 1) nostress-whitening or deformation; 2) torn edges are consistent andpropagate cleanly; 3) the tear propagates in a straight line from thenotch across the width of the sheet parallel to the machine direction;4) tear would restart easily and propogate cleanly if interrupted. Ifthe tear initiation at the notch shows stress-whitening or deformation;and/or the tear propogation is ragged, or is non-linear or non-parallelto the machine direction of the film, is propogated at an angle to themachine direction edge of the film; then this in considered to beunacceptable for directional or linear tear properties. Tear quality wasrated qualitatively as follows:

1=Excellent linear tear property

2=Acceptable linear tear property

3=Marginal linear tear property

4=No linear tear property

Wetting tension of the surfaces of interest was measured substantiallyin accordance with ASTM D2578-67. In general, the preferred value was anaverage value equal to or more than 40 dyne/cm with a minimum of 38dyne/cm.

This application discloses several numerical ranges in the text andfigures. The numerical ranges disclosed inherently support any range orvalue within the disclosed numerical ranges even though a precise rangelimitation is not stated verbatim in the specification because thisinvention can be practiced throughout the disclosed numerical ranges.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. Finally,the entire disclosure of the patents and publications referred in thisapplication are hereby incorporated herein by reference.

In the embodiment of a 2-layer laminate film structure, the (A)-layercould include a sealant layer on one side of a core layer (B).Preferably, this core layer (B) includes a polyolefin resin-containinglayer which in turn, includes a propylene homopolymer or propylenecopolymer. More preferable is an ethylene-propylene impact copolymer.The (A)-layer can be the same thickness as the (B) core layer, butpreferably is thinner than the (B)-layer, about 5-50% of the totalthickness of the (A) and (B) layers combined, more preferably 10-30% ofthe total thickness of the laminate film structure (A) and (B) layerscombined. This core polyolefin resin-containing layer can also includean antiblock component selected from the group consisting of amorphoussilicas, aluminosilicates, sodium calcium aluminum silicates, glassmicrospheres, talcs, micas, minerals, crosslinked silicone polymers, andpolymethylmethacrylates to aid in machinability and winding. It can alsobe contemplated to discharge-treat the side of the core layer (B)opposite the heat sealable layer (A) in order to enhance that side forlaminating via adhesives, etc. Discharge-treating can be done by any ofseveral means well known in the art, such as corona, flame, plasma, ordischarge-treatment in a controlled atmosphere of selected gases.

In the embodiment of a 3-layer laminate film structure, a third layer(C) could be disposed on the side of the core layer (B) opposite theheat sealable layer (A) and preferably includes a polyolefinresin-containing layer which in turn, includes a polyolefin selectedfrom the group consisting of propylene homopolymer, copolymers,terpolymers, polyethylene, maleic anhydride-grafted polyolefins, andcombinations thereof. This third polyolefin resin-containing layer canalso include an antiblock component selected from the group consistingof amorphous silicas, aluminosilicates, sodium calcium aluminumsilicates, glass microspheres, talcs, micas, minerals, crosslinkedsilicone polymers, and polymethylmethacrylates to aid in machinabilityand winding. The third polyolefin layer can also be a discharge-treatedlayer having a surface for lamination, metallizing, printing, or coatingwith adhesives or inks as described previously.

In the case of a film structure including only one layer, such as theheat sealable layer (A), as mentioned previously, it can be contemplatedto discharge-treat one side of this layer for lamination, metallizing,printing, or coating, while leaving the opposite side untreated in orderto maintain heat sealable properties. Discharge-treating this layer canresult in the treated side having a narrower seal range due tocrosslinking of the ethylene and/or butene constituents of the blend.Thus, at least one side should be left untreated in order to obtain thefull and useful heat seal range. In the case of a 2-layer (or more)laminate structure wherein the sealable layer (A) is contiguous with apolyolefin core layer (B), it is preferable to discharge-treat the sideof the core layer opposite the sealable layer (A) for purposes oflaminating, printing, metallizing, coating, etc.

Discharge-treatment in the above embodiments can be accomplished byseveral means, including but not limited to corona, flame, plasma, orcorona in a controlled atmosphere of selected gases. Preferably, in onevariation, the discharge-treated surface has a corona discharge-treatedsurface formed in an atmosphere of CO₂ and N₂ to the exclusion of O₂.The laminate film embodiments could further include a vacuum-depositedmetal layer on the discharge-treated layer's surface. Preferably, themetal layer has a thickness of about 5 to 100 nm, has an optical densityof about 1.5 to 5.0, and includes aluminum. In one variation, thelaminate film is an extruded laminate film.

In yet another embodiment, this invention provides monoaxially orientedpolyolefin films with a heat sealable layer of blends of propylenerandom copolymers, elastomers, and plastomers with low densitypolyethylene to enhance heat sealing properties for flexible packagingpurposes. An additional embodiment provides laminate structures of theheat sealable polyolefin blend layers for heat sealable applications inflexible packaging.

Preferably, the monoaxially oriented film is produced via extrusion ofthe heat sealable layer blend through a die whereupon the molten filmlayer is quenched upon a chilled casting roll system or casting roll andwater bath system and subsequently oriented in the machine direction andannealed or heat-set to minimize thermal shrinkage into a thermally,dimensionally stable film.

In the embodiments of a multi-layer film, the laminate film is producedvia coextrusion of the heat sealable layer blend and the core layerand/or other layers through a compositing die whereupon the moltenmultilayer film structure is quenched upon a chilled casting roll systemor casting roll and water bath system and subsequently oriented in themachine direction and annealed or heat-set into a multi-layer film.

All these examples can also be metallized via vapor-deposition,preferably a vapor-deposited aluminum layer, with an optical density ofat least about 1.5, preferably with an optical density of about 2.0 to4.0, and even more preferably between 2.3 and 3.2. In the embodiments inwhich the invention is part of a multi-layer coextruded film, the metalreceiving layer or surface may be specially formulated ordischarge-treated to enhance metal deposition, metal nucleation, andmetal adhesion properties.

This invention provides a method to improve the heat sealability ofmonoaxially oriented films resulting in an economical, highly sealablefilm with excellent directional tear properties suitable for packagingapplications. The invention helps solve the problems associated with theprior art of directional tear polyolefin substrates in packagingapplications.

This application discloses several numerical ranges in the text andfigures. The numerical ranges disclosed inherently support any range orvalue within the disclosed numerical ranges even though a precise rangelimitation is not stated verbatim in the specification because thisinvention can be practiced throughout the disclosed numerical ranges.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. Finally,the entire disclosure of the patents and publications referred in thisapplication are hereby incorporated herein by reference.

1. A monoaxially oriented polyolefin film that exhibits excellent lineardirectional tear characteristics in a direction parallel to theorientation direction comprising: a first layer comprising apropylene-based random copolymer, and at least about 3.0 wt % of a lowdensity ethylene homopolymer, wherein the first layer is heat sealableand monoaxially at least 2.5 times in one direction.
 2. The monoaxiallyoriented polyolefin film of claim 1, wherein the propylene randomcopolymer is an ethylene-propylene random copolymer.
 3. The monoaxiallyoriented polyolefin film of claim 1, wherein the first layer comprisesan ethylene-propylene random copolymer and an ethylene-propylene-butenerandom copolymer.
 4. The monoaxially oriented polyolefin film of claim1, wherein the film is a single layer film.
 5. The monoaxially orientedpolyolefin film of claim 1, further comprising a second layer comprisinga polyolefin resin on a side of first layer.
 6. The monoaxially orientedpolyolefin film of claim 5, wherein the second layer comprises anethylene-propylene impact copolymer.
 7. The monoaxially orientedpolyolefin film of claim 5, further comprising a third layer comprisinga polyolefin resin on a side of the second layer opposite the side withthe first layer.
 8. The monoaxially oriented polyolefin film of claim 1,wherein the first layer comprises at least 50 wt ethylene-propylenerandom copolymer.
 9. The monoaxially oriented polyolefin film of claim1, wherein the first layer comprises 3-30 wt % low density ethylenehomopolymer.
 10. The monoaxially oriented polyolefin film of claim 1,wherein the first layer further comprises an antiblock componentselected from the group consisting of amorphous silicas,aluminosilicates, sodium calcium aluminum silicates, glass microspheres,talcs, micas, minerals, crosslinked silicone polymers, andpolymethylmethacrylates.
 11. The monoaxially oriented polyolefin film ofclaim 1, wherein a side of the first layer is discharge treated.
 12. Themonoaxially oriented polyolefin film of claim 1, wherein the first filmlayer is monoaxially oriented from 4.0 to 6.0 times in a machinedirection.
 13. The monoaxially oriented polyolefin film of claim 5,wherein the first layer is 5-50% of the total thickness of the firstlayer and the second layer combined.
 14. The monoaxially orientedpolyolefin film of claim 5, wherein the second layer comprises anantiblock component selected from the group consisting of amorphoussilicas, aluminosilicates, sodium calcium aluminum silicates, glassmicrospheres, talcs, micas, minerals, crosslinked silicone polymers, andpolymethylmethacrylates.
 15. The monoaxially oriented polyolefin film ofclaim 5, wherein a side of the second layer opposite the first layer isdischarge-treated.
 16. The monoaxially oriented polyolefin film of claim1, further comprising a metal layer.
 17. A flexible packaging comprisingthe monoaxially oriented polyolefin film of claim
 1. 18. A monoaxiallyoriented polyolefin film that exhibits excellent linear directional tearcharacteristics in a direction parallel to the orientation directioncomprising: a first heat comprising an ethylene-propylene randomcopolymer, and at least about 3.0 wt % of a low density ethylenehomopolymer, wherein the first layer is heat sealable and monoaxially atleast 2.5 times in one direction.
 19. A monoaxially oriented polyolefinfilm that exhibits excellent linear directional tear characteristics ina direction parallel to the orientation direction comprising: a firstheat comprising an ethylene-propylene random copolymer, anethylene-propylene-butene random copolymer, and at least about 3.0 wt %of a low density ethylene homopolymer, wherein the first layer is heatsealable and monoaxially at least 2.5 times in one direction.
 20. Amethod of making a monoaxially oriented polyolefin film that exhibitsexcellent linear directional tear characteristics in a directionparallel to the orientation direction comprising: extruding a heatsealable first layer comprising a propylene random copolymer, and atleast about 3.0 wt % of a low density ethylene homopolymer; andorienting the first layer at least 2.5 times in one direction.
 21. Themethod of claim 20, wherein the propylene random copolymer is anethylene-propylene random copolymer.
 22. The method of claim 20, whereinthe first layer comprises an ethylene-propylene random copolymer and anethylene-propylene-butene random copolymer.
 23. The method of claim 20,wherein the film is a single layer film.
 24. The method of claim 20,further comprising coextruding a second layer comprising a polyolefinresin with the first layer.
 25. The method of claim 24, wherein thesecond layer comprises an ethylene-propylene impact copolymer.
 26. Themethod of claim 24, further comprising coextruding a third layercomprising a polyolefin resin on a side of the second layer opposite theside with the first layer.
 27. The method of claim 20, wherein the firstlayer comprises at least 50 wt % ethylene-propylene random copolymer.28. The method of claim 20, wherein the first layer comprises 3-30 wt %low density ethylene homopolymer.
 29. The method of claim 20, whereinthe first layer further comprises an antiblock component selected fromthe group consisting of amorphous silicas, aluminosilicates, sodiumcalcium aluminum silicates, glass microspheres, talcs, micas, minerals,crosslinked silicone polymers, and polymethylmethacrylates.
 30. Themethod of claim 20, further comprising discharge treating a side of thefirst layer.
 31. The method of claim 20, wherein the first film layer ismonoaxially oriented from 4.0 to 6.0 times in a machine direction. 32.The method of claim 24, wherein the first layer is 5-50% of the totalthickness of the first layer and the second layer combined.
 33. Themethod of claim 24, wherein the second layer comprises an antiblockcomponent selected from the group consisting of amorphous silicas,aluminosilicates, sodium calcium aluminum silicates, glass microspheres,talcs, micas, minerals, crosslinked silicone polymers, andpolymethylmethacrylates.
 34. The method of claim 24, further comprisingdischarge treating a side of the second layer opposite the first layer.35. The method of claim 20, further comprising vapor depositing a metallayer on the film.